1. Field of the Invention
The invention relates to pneumatic percussive tools used in the construction and mining industries, mechanical engineering and metallurgy, and more specifically, it deals with single-blow pneumatic percussive tools.
2. Description of the Prior Art
Pneumatic percussive tools, in particular, pneumatic hammers are used for marking, center-popping, riveting, marking-out and gate trimming. Depending on a specific application, the pneumatic hammer has a working tool such as a stamp, center punch or chisel. The working tool is mounted in a casing having an interior space and inlet and outlet ports. The interior space of the casing accmmodates a hammer piston defining working chambers in the interior space. An energy carrier is gaseous fluid under pressure which is supplied to the tool from a portable or stationary compressor along a flexible hose. During operation of the tool, the hammer piston axially reciprocates under the action of compressed air alternately admitted to the working chambers through the air distribution device to impart a blow to the end face of the working tool at every working cycle. The working tool performs work under the action of blows whereby, depending on the type of the working tool, marking, center-popping, trimming or riveting takes place.
Since operations performed using such tools are effected with the direct participation of the operator, stringent requirements are imposed upon their reliability (durability) and operating conditions.
Known in the art is a single-blow pneumatic percussive tool (cf. USSR Inventor's Certificate No. 706239, Int.Cl. B 25 D 9/04), comprising a hollow cylindrical casing having inlet and outlet ports accommodating a hammer piston having an opening and dividing the interior space of the casing into upper and lower chambers, and a spring-biased working tool having a head in the form of a valve mounted on the side of the lower chamber for establishing communication thereof with atmosphere when the hammer piston moves downwards.
For starting the tool, i.e. for causing the hammer piston to move down, it is necessary that the lower chamber communicate with atmosphere. In this tool such communication is possible when the working tool is pressed against the workpiece surface so that the head in the form of a valve provides for communication of the lower chamber with atmosphere. However, big effort is needed on the part of the operator for starting the tool so that operating conditions are complicated and impact energy decreases.
Known in the art is a single-blow pneumatic percussive tool (cf. USSR Inventor's Certificate No. 1027026, Int. Cl. B 25 D 9/04, comprising a hollow cylindrical casing having inlet and outlet ports and accommodating a hammer piston which divides the interior space of the casing into upper and lower working chambers, a working tool, a sleeve with ports mounted in the casing for movement relative thereto, and a starting device in the form of a spring-biased valve mounted on the side of the lower chamber.
The lower chamber should communicate with atmosphere to effect the hammer piston movement downwards. In this tool, this is achieved by pressing against the working tool so that the latter is caused to move until it bears against the sleeve. However, in orer to move the sleeve to such an extent that the lower chamber might communicate with atmosphere through the sleeve ports and the tool might be started, the force applied to the working tool must be great enough. Since the tool is started by the operator, great forces should be applied thus complicating operating conditions and lowering impact energy of the tool.